How do I add a new client (Company) in Modulr Accounts Payable?

You can add new clients from the Manage Companies page in Accounts Payable.

Select your company name in the top left of the main screen
Select 'Manage companies' from the list
You'll see your list of companies
Select 'Add Company' in the top right
Choose whether it's a Company or Individual you are adding
If it's a company – start typing the company name and select it from the list that appears in the company lookup
Complete the rest of the details asked:
1. Number of employees
2. Website address (this will help us to create a unique intake email address for this company)
Select 'Add Company'
Finally, connect the Accounting software you want to use with this company (see here for more details)