Our agency says we need an 'API integration' to connect our invoicing system — what does that mean, and what should I ask for?

An API is just a digital handshake between two software systems, but the moment one side updates, that handshake can break. If your invoicing software changes a parameter tomorrow, the agency shouldn't be able to turn around and say "that's a new feature request, we'll invoice you extra." If you're paying 150 euros a month, version updates must be fully covered.

15 hours of staff time a week comes out to 60 hours a month. When you factor in hourly wages and social security costs in Spain, manual entry is costing you at least 800 to 900 euros every month. If the integration runs smoothly, an 1,800-euro investment pays for itself in two and a half months.

Before signing anything, check your invoicing software's official website. Most popular platforms already offer official, off-the-shelf plugins for major e-commerce setups. If a ready-made plugin exists, you can solve this for 20-30 euros a month instead of paying an agency to build something from scratch.

That 150 euros a month maintenance fee is a classic agency move: build it once, kick back, and bill you every single month. Make sure the proposal details exactly what service you're getting for that 150 euros during months where nothing goes wrong.

Ask the agency to state in writing in the technical spec whether they're using webhooks or scheduled cron jobs. Webhooks issue invoices in real time. Also, tax ID validation (VIES / NIF checks) should be verified through a filter before anything ever hits the API.

Adding a GDPR compliance clause to your contract is a legal requirement. Since customer identity and address data will be transmitted between two servers, the agency acts as a data processor and must assume liability for any potential security vulnerabilities on their end.

Manually entering 500 invoices a month is an absolute nightmare of a workload. Dont let the upfront setup cost scare you off; if you get it hooked up under a solid contract, youll see it was worth every penny of saved time and stress within the very first week.

This is exactly what we experienced. Don't hesitate to ask; those who don't ask always pay more.

If you get three different answers on a topic, the question was asked wrong. Hope this helps.

Same here. Hasty decisions become decisions you have to fix six months later.

Solutions that work at a small scale collapse when you grow; I learned this late. That's all, sorry if I went on too long.

This thread is archived. Weekly written progress reports are much more useful than asking for dates.

Good luck with that.

This approach has a cost, which isn't discussed. Ask who prepared the quote and who will actually do the work.

When we decide without measuring, we always end up in the same place. Of course, it varies if your situation is different.

Thanks a lot, I'll try it today.

Correct.

I feel the same way. Everyone rushing into api web development integration gets stuck at the same point.

There's one point I'm curious about. Code without setup documentation isn't yours, even if you have it.

The biggest time-waster for us was not knowing who had the final say. That's all, sorry if I went on too long.

correct in theory, but it doesn't work that way in practice and i mean trying to do this alone is the most expensive way.

prroven by experience.

Saved. If you don't write this down from the start, it leads to arguments later.

If you post the result here, it will help others too.

Great work. When making decisions, write down the worst-case scenario too, not just the best.

If you have questions, write them; I'll answer as best I can.