Specify the Callback requirements as in platformio there are more than one.

[EmileSpecialProducts]

Library Manager: Warning! More than one package has been found by Callback requirements:
Library Manager: - tomstewart89/Callback@1.1
Library Manager: - harry-obrien/Callback@1.0.0
Library Manager: - pippijn/Callback@0.1

library.properties
depends=NimBLE-Arduino,tomstewart89/Callback