You need to use a tpl trick to interpolate the value, since helm variable in values are not processed, you have to update your deployment, for example:
In your values.yaml: ... tag: "{{ .Chart.AppVersion }}" ...
In your deployment: ... image: "{{ .Values.api.image.repository }}:{{ tpl .Values.api.image.tag . }}" ...
Found in issue referenced here helm/helm#2514