The verdict in three sentences
A custom connector to the Xero or QuickBooks Online API costs, as a 2026 order of magnitude, 2,500 to 6,000 EUR excl. VAT in the Dublin market and ships in 3 to 6 weeks. It removes 3 to 8 hours of manual re-keying per week for an SME finance team, worth several thousand euros of admin time a year. The real value sits in error handling and the sync log, far more than in the API call itself.
What the connector actually has to do
The classic scenario for a Dublin CFO: the project management app records billable hours, approved milestones and rechargeable expenses, then someone re-keys everything into Xero or QuickBooks at the end of the week or month. The connector has to push contacts, sales invoices and time lines automatically, then pull back the payment status so project managers know who has paid.
Both Xero and QuickBooks Online expose REST APIs secured with OAuth 2.0, with resources for contacts or customers, invoices, items and journals. Rate limits and app approval rules apply: check them during scoping, before you sign anything.
| Flow to automate | Accounting API resource | Frequency | Expected error handling | Estimated effort |
|---|---|---|---|---|
| Create or update customer | Contacts (Xero) or Customers (QBO) | when the project is created | de-duplication by company number, automatic retry | 1 to 2 days |
| Sales invoice | Invoices | when the milestone is approved | VAT rate checks, numbering, queue | 3 to 5 days |
| Billable hours | Invoice lines and items | weekly | aggregation per project, rounding rules | 2 to 4 days |
| Payment status | Invoices (read) | hourly | scheduled polling or webhooks, matching by ID | 1 to 3 days |
| Credit notes | Credit notes | on demand | mandatory link to the original invoice | 1 to 2 days |
| Tracking categories | Tracking categories or classes | monthly | mapping project codes to accounts | 1 to 2 days |
| Sync log | inside the app | permanent | timestamps, manual replay, email alert | 2 to 3 days |
The sync log is the line cheap quotes forget. Without it, an invoice rejected for a wrong VAT rate (23 %, 13.5 %, 9 % or 0 % in Ireland) disappears silently and the CFO finds it at month-end close. Demand a screen listing every push, its status, the error message returned by the API and a replay button.
Custom build or Zapier and Make: 2026 comparison
No-code tools work for low volume and simple logic. Once you pass 50 to 80 invoices a month, aggregate hours per project or handle credit notes, scenarios become fragile and expensive to watch.
| Option | Upfront cost | Monthly cost | Reliability | Main limits |
|---|---|---|---|---|
| CSV export and manual import | 0 EUR | 3 to 8 h of data entry per week | 2 to 5 % re-keying errors | no real time, depends on one person |
| Zapier (Team plan) | 500 to 1,500 EUR setup | 70 to 110 EUR | medium, little error recovery | task caps, limited conditional logic |
| Make | 500 to 1,500 EUR setup | 20 to 60 EUR | medium | scenarios hard to maintain at volume |
| Custom connector (market range) | 2,500 to 6,000 EUR excl. VAT | 75 to 200 EUR maintenance | high, replay and alerts | quality varies by vendor |
| Kolonell: connector inside a custom app | simple app 2.5 to 4 M FCFA (3,810 to 6,100 EUR) | Standard maintenance 75,000 FCFA (110 EUR) | high, log and replay included | scope fixed in the quote |
A typical schedule fits in six weeks: week 1 scoping, sandbox access and field mapping; weeks 2 to 4 building the flows and the log; week 5 acceptance testing on one month of real data; week 6 go-live with double checks on the first invoices. A connector limited to customers and invoices can drop to 3 weeks.
What to demand in the quote
Four points separate a connector that lasts from one that breaks at the first API change: a written list of flows and fields, the error recovery strategy (number of retries, delay between attempts), log access for the finance team, and a maintenance clause covering API changes and token renewals. Kolonell's monthly maintenance plan at 75,000 FCFA (110 EUR) covers monitoring, fixes and minor adaptations.
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Aoife, CFO of a 45-person engineering consultancy in Dublin, has about 6 hours a week of invoices and hours re-keyed. At a loaded hourly cost of 38 EUR, that is 228 EUR a week, or 10,488 EUR over 46 working weeks. The connector is quoted at 4,500 EUR excl. VAT, plus 110 EUR monthly maintenance (1,320 EUR a year). First-year cost: 5,820 EUR, net saving of about 4,670 EUR. The upfront investment pays back in just over 5 months, before counting fewer billing errors.
FAQ
Do Xero and QuickBooks open their API to every subscriber?
Yes, through OAuth 2.0 apps, but rate limits apply (Xero allows around 60 calls per minute per tenant). Plan half a day of scoping to validate access and the sandbox before development starts.
How long does delivery take?
Between 3 and 6 weeks depending on the number of flows. Customers and invoices only: about 3 weeks; with hours, credit notes and tracking: 5 to 6 weeks.
What happens when the API changes?
Monthly maintenance covers monitoring and adaptations, usually 2 to 4 hours a month. At Kolonell, the Standard plan is 75,000 FCFA (110 EUR) a month.
Can the connector handle several VAT rates on one invoice?
Yes, provided the rates (23 %, 13.5 %, 9 %, 0 %) are carried by each line in the business app. The connector checks consistency before pushing and cleanly rejects incomplete cases.
Is Zapier enough?
Below 50 invoices a month with no time aggregation, yes, for 70 to 110 EUR a month. Beyond that, the lack of a reliable log and replay quickly costs more than a custom build.
Let's scope your project. Send us the list of flows you need into Xero or QuickBooks: we price the connector, the maintenance and the go-live date. Detailed quote within 48 h. WhatsApp +221 77 596 93 33 or request a free quote.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
