They are probably Activation Locked. I had to go through this process a few times and documented the steps as well as notes from speaking with Apple Support. This was recent as of early 2022. As @afnpw noted, it takes awhile for it to be processed, around 3 weeks. It can be hard to locate documentation for purchase if the device is lets say 5 years old. Your purchaser can usually provide you with a purchase number for bulk purchases.
You can prevent this by enabling Prevent user from enabling Activation Lock in Devices > PreStage Enrollments.
- Go to https://al-support.apple.com and under Need Additional Support click Get started.
- Accept agreement and fill in the request with your email address and the serial number of the device.
- Click continue
- Wait for Apples confirmation email to appear in your inbox with the subject “Please verify you Contact Information.” Usually this is instant.
- Click confirmation link to open the Request page.
- Fill out all require fields
- First Name
- Last Name
- Original Purchase Date YYYY-MM-DD
- Where did you originally purchase your device (Store Name)
- Store Country/Region
- Store Address 1
- Store Address 2 (optional)
- Store City
- Store State
- Store Postal Code
- Website (optional)
Please provide your proof of ownership (see note below regarding Proof of ownership) below, such as a photo or screenshot of the original sales receipt. The document must reflect the purchase of an Apple product and show the product’s identifying information, such as a serial number, IMEI, or MEID. Acceptable file types include: PDF, JPEG, PNG, PSD, HEIC, and TIFF.
Proof of ownership: Apple said this could be a Sales receipt or invoice, Bank or credit card statement (with personal information and unrelated transactions made illegible), Wireless carrier contract if it was a cellular iPad or Shipment packing list showing the IMEI or serial number.
- Upon submitting, Apple will email you the 9-digit Apple Support case number for your records.
Things to note
- You cannot bulk submit requests, they must be submitted one by one with required documents/info
- If your email address was used to submit a request and the Apple Support case has not been processed, attempting to submit additional request will give the error “We found an existing case for the email address provided. You can submit only one request per email address.”