Contact
Email contact@valab.gg and a person reads it. That is the whole of the support system, which is honest about the size of the project rather than a ticket queue pretending to be a department.
What to include
For a replay that will not process, the match id is the single most useful thing: it is the filename of the .vrf, and it is in the URL of the match page if the upload got that far. Run the file through the .vrf inspector first if you can. It reads the file in your own browser and will usually say plainly whether the file is intact and whether it came from a build valab knows, which answers most of these before an email is needed.
For a billing question, the email address on the account is enough. Do not send card details; nobody here can use them and they should not be in an inbox.
Bugs and wrong numbers
A number that looks wrong is worth reporting even if you are not sure. This whole tool is built on a file format that was worked out by measurement, and the most useful bug reports have been people saying a stat did not match what they remembered happening. Say which match, which round, and what you expected instead.
Press and creators
Same address. If you want to show valab to an audience, say so and you will get an account with a raised allowance so you are not fighting the free tier while recording.