When testing your integration with OptimizeMember, you get an error like "unable to modify subscription" after payment.
How to fix:
This is usually because you are testing your site when logged in as an administrator user. This means that when you purchase, the OptimizeMember system tries to modify your existing user account which cannot be done - the system will not allow you to modify the subscription of that account
If you test on a new browser (different browser to the one you are logged into your site with) then you should find this resolves the issue. To be sure, if you also clear the cookies/cache/temporary files of that browser and then test your process you should get the exact process of a new customer
In some rare ocassions this issue can also be generated if you have created a custom order link URL for buttons (such as pricing table buttons) rather than using our button creators. If you do create your own order link URLs, ensure that you remove any references to "Referencing Customer" or IP address such as:
Remove any codes like this to ensure you do not get any errors when processing payments. Always test your payment buttons or have a friend test them when logged out of your site on a clean browser (clear cookies and cache first)