In most cases, it is not possible, because the guarantor (sponsor) must be present at the immigration office for the extension of the B211A visa. Most people are not able to obtain a B211A visa through the Indonesian embassy in their home country.
If you received your B211A visa from us, then we would need to submit your passport for the extension. If you received your B211A visa from an embassy, then you would be able to extend it yourself. However, most people still choose to an agency service like ours to do the extension since it saves time and you can focus on things you like and don’t have to go to the immigration office 2-3 times for each extension.