If you are filling invoices for more than $600 USD (or equivalent) per year to a Collective with a Fiscal Host in the US (such as the Open Source Collective), you will need to send them one of these forms:
Reimbursed expenses don't count toward the $600 limit, only invoices.
For tax purposes, you will essentially be treated as an independent contractor. If your host is in the US, you will be issued a 1099 if your earnings exceed $600. Here's a good explanation of how W-9s work for independent contractors, and there's more info on what a 1099 is here.
If you don’t meet the $600 threshold, simply report your earnings as miscellaneous self-employment income when you file your taxes.
Open Collective has a little robot that helpfully puts a comment on expenses that go over the limit (for Collectives we host), reminding you about the tax form. Sometimes the little robot makes mistakes, but it's trying to be helpful!
If you are being paid by a Collective with a Fiscal Host not managed by Open Collective or located in another country, please get information about tax requirements directly form them. You should consult an accountant to get informed about any tax or reporting obligations that apply.
Collectives that live under the umbrella of a Fiscal Host, don't need to worry about accounting and tax obligations, because the host manages that (this is the awesome value of fiscal hosting). If you need tax or accounting information for some reason, get in touch with your fiscal host.
Some Collectives run their own Fiscal Host, and they have all the normal tax and reporting obligations of any legal entity. In that case, consult with your accountant to understand the requirements for taxes.