Unable to add messages dynamically on Absence record page

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We have a requirement where HR should be able to write a meaningful message and that message should get displayed on Absence Record page for ESS.

For example, HR writes a message 'Attachment required: Hospital Prescription or Medical Certificate' for Sick Leave absence and this message should get displayed when employee tries to add Sick Leave.

We have tried to achieve this through page composer. But in that case, the message becomes static.

How can we achieve this feature so that HR can add the messages dynamically?

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