Hello Mark,
The Customer Card is the correct place to enter a credit limit. I cannot reproduce this same situation you are seeing, the Credit Limit field is editable for me, so I have a few questions to help us track down why your window is behaving differently.
1. Does this happen on every Customer?
2. What about a new Customer, can you set the Credit Limit on a new Customer?
3. Do you have any other Companies, does this same situation happen in other companies?
4. What about in Cronus sample company, can the Credit Limit field be edited in that company?
5. Do you have a workflow enabled for Customer Approvals?
Please let me know what you find out regarding these questions.
Thank you.
Jennifer Reinhardt
Please see our Dynamics 365 Financials Support Team Blog for helpful information:
blogs.msdn.microsoft.com/dyn365finsupport