Advise on visa application process: Tier 2 dependent visa application (applying at the same time as the main applicant)

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During a UK tier 2 dependent visa application (applying at the same time as the main applicant), It is asking the visa expiring date of the main applicants for IHS payment. What shall I provide there?

Further explanation:
I wish to bring my family along with me to UK, hence we would like to apply the UK Tier 2-General VISA together with my wife and daughter.
As per available information on Welcome to GOV.UK, each applicant and dependent will need to submit a separate application.
I have filled the application and paid IHS and visa fees.
Now during the application of my wife, before IHS payment they are asking the visa expiring date of the main applicants. What should i put there?

Many thanks for your help and comments.