I just tried something myself and experienced some challenges but I found a way around it.
When others are trying to add you, have them try this:
go to the "People" area
click on the "+ People" button
change the "Add user(s) by" option to "Login ID" (I believe it defaults to "Email Address")
NOTE: for Canvas "Free for Teachers" (and possibly at individual institutions, depending on their setup), a Canvas user account's email address and login ID are the same)
have them enter your email address
set the "Role" to "Teacher" (or the desired role)
select other other desire options
click on the "Next" button
NOTE: your account should have been found and be displayed
Are all of you using Canvas Free for Teachers or the paid-for version of Canvas at your school?
Are the others that are trying to add you, trying to create a Canvas user account for you or trying to use a Canvas user account that you already have?
Is the email address that they are trying to use formatted correctly and without any spaces or extra characters?
Hello. Yes, we are all using Canvas Free for Teachers. They are trying to add me using the account I already have. We triple-checked the email address, and it is the correct one.
I just tried something myself and experienced some challenges but I found a way around it.
When others are trying to add you, have them try this:
go to the "People" area
click on the "+ People" button
change the "Add user(s) by" option to "Login ID" (I believe it defaults to "Email Address")
NOTE: for Canvas "Free for Teachers" (and possibly at individual institutions, depending on their setup), a Canvas user account's email address and login ID are the same)
have them enter your email address
set the "Role" to "Teacher" (or the desired role)
select other other desire options
click on the "Next" button
NOTE: your account should have been found and be displayed
