Sending push notification to exernal_users does not work anymore

[mdismer]

When using "include_external_user_ids" I'm getting this error:

could not send push notification Platforms You may only send to one delivery channel at a time. Make sure you are only including one of push platforms, Email, or SMS.

According to the API documentation "channel_for_external_user_ids" must be set to 'push', 'email' or 'sms', but the gem doesn't seem to support this.

[MatteoJoliveau]

Hi @mdismer, thank you for reporting this! Are you willing to submit a PR to add support for this field?