Database design -relation among entities -

i have:

• request has id pk , other attributes.

• customer database id pk , other attributes

• visitor entity , phone number can pk.

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• customer , visitor can make request.
• i need record whom make request
• the customer id has different format phone number.
• i add fk called requestid inside visitor table , make pk visitor identified request.
• but problem how connect customer request?
• my suggested solutions:
• add fk inside customer table ---> can not change database
• creating new table , copy customer info , adding new column --> contains redundancy.
• create new table contains requestid , customerid ---> relation not many-to-many make in separate table(customer can make many request , request made 1 customer) , don't no if god practices.
• add fk inside request table identified whom make request ---> problem domain not same.

kindly see image entities , tell me best way connect customer?

thanks in advance,

if customer can make many requests, , request can belong 1 customer, need foreign key in request reference customer.

if customer can associated many visitors, visitor should have foreign key customer. you'd think of visitor join table make customer requests.