@Ahmed Jalamneh Thank you for reaching out to us, As I understand you are trying to activate the P2 premium free trial, during the process you are getting error 43881.
Researched on this error code and noticed few cases internally regarding this error, this can be resolved by contacting our support - https://support.microsoft.com/en-gb/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2 based on your country code select the appropriate contact number and get a case created with our subscription team further they will validate your details using and further you will be able to activate the P2 premium free trial.
Let me know if you have any further questions, feel free to post back.
Please remember to "Accept Answer" if answer helped, so that others in the community facing similar issues can easily find the solution.