If you have more than one data file to provide you need to create one account for each (which means that you will receive one invite for each).
When creating your company accounts, use the same password in the first step.
Then, confirm your company and accounting application details.
It will allow you to access all your company accounts from the same user account through the "change company" button :
When uploading your data file, you can check the company account to which you are uploading at the top right corner of your screen.
If this is not the correct one, cancel the upload, click "change company" and click to select the expected one.