Cannot add ppa:graphics-drivers

Question

I tried to execute sudo add-apt-repository ppa:graphics-drivers/ppa to install the latest GTX 1070 driver as explained here

This command ended up with an error:

Get:12 http://packages.blackfire.io/debian any InRelease [23.2 kB]
Err:12 http://packages.blackfire.io/debian any InRelease

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 696DBE66A72D76DA Fetched 23.2 kB in 3s (8,640 B/s)

Reading package lists... Done W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.blackfire.io/debian any InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 696DBE66A72D76DA W: Failed to fetch http://packages.blackfire.io/debian/dists/any/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 696DBE66A72D76DA W: Some index files failed to download. They have been ignored, or old ones used instead.

Then I added the PUBKEY with

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 696DBE66A72D76DA

as explained here.

Now I get this error:

Get:12 http://packages.blackfire.io/debian any InRelease [23.2 kB]

Reading package lists... Done E: Repository 'http://packages.blackfire.io/debian any InRelease' changed its 'Origin' value from 'packagecloud.io/sensiolabs/sensiolabs' to 'packagecloud.io/blackfire-io/stable' E: Repository 'http://packages.blackfire.io/debian any InRelease' changed its 'Label' value from 'sensiolabs' to 'stable' N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

How can I solve this issue?