Currently we can't pass pipeline variables for custom pipelines to schedule jobs, so if that functionality can be added that would be great.

If that we can do by with the API only like below:-

curl -X POST -is -u UID:PWD \
-H 'Content-Type: application/json' \
https://api.bitbucket.org/2.0/repositories/repo1/slack/pipelines_config/schedules/ \
-d '

{ "type":"pipeline_schedule", "uuid":"\{714a83a6-9064-495e-97ce-db28e3848a87}

",
"enabled":true,
"target":{
"type":"pipeline_ref_target",
"ref_type":"branch",
"ref_name":"test",
"selector":

{ "type":"custom", "pattern":"sonar" }

,
"variables": [

{ "key": "BITBUCKET_DEPLOYMENT_ENVIRONMENT", "value": "test" }

]
},
"cron_pattern":"15 * * * * ? *",
"created_on":"2020-07-23T15:17:10.661Z",
"updated_on":"2020-07-23T16:32:11.13Z"
}'