Some countries have special restrictions related to acquiring their numbers, and they request special documents, like proof of address, registration documents..etc.
Once you start buying a number, and choosing a country that needs special documents, you will get a note if the number is available ,and you will get a note asking you to submit the documents, please refer to the image below:
Once you submit your documents, your number will show under Numbers section as pending, and you will get notified once approved.
Have any questions? You can always contact our Support Team at firstname.lastname@example.org.