Hi @Harj, I’m so sorry we missed your message on that article previously!
I’ve moved your message out into a new topic so we can address it separately. It’s been a very long while since you reached out so I expect you may have got this figured out but I wanted to still address the questions asked here in case it’s helpful to others that may come across this thread!
I have created a multi select Person field called Interested Service in Pipedrive and I'm trying to append the value from the Deal Interested Service field to the Person Interested Service field. However when I tested this, the zap did not append the details from the Deal but also removed the existing value in the Person record in PD.
It appears that Interested Service field is being rendered in the Zap as a Dropdown Menu field so the approach in that article Nick wrote won’t work as only a single value can be passed to that type of field. There’s an existing feature request for the ability to select multiple values for a multi-selection field like that “Interested Service” field so I’ve added your vote to that. I can’t make any promises around when/if that will get sorted but we’ll be sure to notify you by email once it is.
In the meantime it might be worth trying the API Request (Beta) action for Pipedrive to see if that allows you to update the multi-select field. That type of action is a bit more advanced as it would require you to reference Pipedrive’s API documentation to ensure the request is set up correctly, but we do have a general guide on using that type of action which may be helpful: Set up an API request action.
Also when trying to map the Interested Service fields in the zap, the Deal value appears as an ID value and for the Person it shows the actual values and not the ID.
It appears that there are differences in how the selected values are referenced between some the Pipedrive triggers and actions. For cases like this you could use a Formatter (Utilities > Lookup Table) action to convert the names into the necessary IDs for the option that needs to be selected. You can find out more about lookup tables here: Create lookup tables in Zaps
Hope that helps. If you have any questions or if there's anything else I can assist with do let me know! 
