Sorry for the delay in response.
It seems that you are trying to Export PDF in Adobe Acrobat Reader DC.
As you get the page to purchase the subscription, try to sign out of the application.
Reboot the device and then sign-in again.
Make sure that you sign in with the email address that you used to purchase the subscription.
Try to export PDF online here https://cloud.acrobat.com/.
Open the link and sign-in with your Adobe ID and password.
Check if you can export PDF there without any issue.
Try the troubleshooting steps provided here in this help document: Troubleshooting Create PDF, Export PDF, Adobe Send, Fill & Sign … services(PDFPack or Document Cloud...
Hope that helps.
If the issue still persists, feel the to update the thread.