Within my Jenkins pipeline I have defined a variable (build number)
Within the task were I create the docker images nd push it to ACR using the ACR Quick Task plugin.
I would like to use that variable as my tag

So my Image name with tag field, looks like
image_name:$VARIABLE

But I get this error:

ERROR: Failed to queue an ACR Quick Task: Some of the properties of 'runRequest' are invalid. InnerErrors: DockerBuildRequest:Image name 'image_name:$VARIABLE' is invalid. \nThe acceptable patterns are 'repository' or 'repository:tag'.The repository and tag names follow the standardized docker repository and tag naming conventions. Tag templates are supported within '{' and '}'.
ERROR: ACR Quick Task ended with HasError
Finished: FAILURE

To check if my variable is set, I created the build step "execute shell" and echo the $VARIABLE and there I get a number:

[task-name] $ /bin/sh -xe /tmp/jenkins6236765085731703135.sh
+ VARIABLE=12

To use the latest tag is not an option