If you are just starting out with Azure then it would be wise for you to take the AZ-900. https://www.microsoft.com/en-us/learning/exam-az-900.aspx This is an optional exam, you do not have to take it, but its good if you are just starting out with Azure.
Now as you say you are an Azure developer, so you will want to take the AZ-203. https://www.microsoft.com/en-us/learning/exam-az-203.aspx After you pass this one exam you will earn the Microsoft Certified: Azure Developer Associate certificate.
You can stop here if you like or go on to the expert level certificates.
I have a video on the Azure exams you can view it @ https://youtu.be/6FPXKF_675A
Hope this helps. Any issues please let me know.