I notice for companies in Tanzania, you should use QB Online Global version
https://quickbooks.grsm.io/Africa
Make sure after you clicked the Trial link or Buy button, you have to find "You're signing up for QuickBooks Online in Tanzania" on top of the screen.
If your clients prefer using QB Desktop, offering them QB Desktop US version with a one-time license. You may purchase the license directly to the company or thru a partner with less price.
And for yourself, consider to upgrade your credential by earning a QuickBooks certification. Imho, ProAdvisor is not relevant to your case. Consider another path (i.e QB Certified User)
https://certiport.pearsonvue.com/Certifications/QuickBooks/Certified-User/Overview.aspx