Issue Zoho CRM API record association

I hope you are doing well

We are implementing ZOHO CRM API to post data from our 570easi.com to ZOHO CRM modules. We have created Module (CustomModule1). We want to make relationship(association) between CustomModule1 record to Contacts module record. For that purpose we have created field in CustomModule1 with

label = Contact

Type of inquiry = contacts

We are making request with following xml

<CustomModule1>
 <row no="1">
      <FL val="Opportunité concernée">48701-Part-Immo-n°1</FL>
      <FL val="CustomModule1 Name">Ressource-48701-Part-Immo-n°1</FL>
      <FL val="CustomModule1 Owner">contact@groupe570.com</FL>
      <FL val="Domaine">Marketing / Communication</FL>
      <FL val="Entreprise familiale">False</FL>
      <FL val="Montant 1">100000</FL>
      <FL val="Profession">Technicien</FL>
      <FL val="Revenu 1">Salaire annuel net (primes, bonus... inclus)</FL>
      <FL val="Secteur d'activité">public</FL>
      <FL val="Type de contrat">CDD</FL>
      <FL val="Vente pour apport">Non</FL>
      <FL val="Contact">Watson SHEEN</FL>
   </row>
</CustomModule1>

In response we are getting following message.

<response uri="/crm/private/xml/CustomModule1/insertRecords">
 <result>
 <row no="1">
 <error>
 <code>4832</code>
 <details>You have given a wrong value for the field : Contact</details>
 </error>
 </row>
 </result>
</response>

We have tried to relate 10-15 different contact with CustomModule1 record. We come to know that some records are associated successfully.

Please guide us why we are not able to associate some contacts with CustomModule1 record.