pass variable to `mutation` apollographql server

I am trying to pass variable to mutation through apollo's javascript client, however, it always returns 400 error: [Error: Response not successful: Received status code 400] which indicates there's something wrong with my query

below is my query:

const SET_ADDRESS_LASTUSED = gql`
  mutation UpdateAddress($phone: String!, $name: String!) {
    updateAddress(input: {
      where: {
        phone: $phone
      },
      data: {
        name: $name
      }
    }) {
      address {
        name
        phone
      }
    }
  }
`;

I am calling the mutation like this:

const [updateLastUsed, updateLastUsedResult] = useMutation(SET_ADDRESS_LASTUSED);

          // sometime later,
          updateLastUsed({
            variables: {
              phone: "+12345678910",
              name: "WhyICanNotChangeMyName?",
            },
          });

is there something wrong that I didn't notice? I'd be able to successfully mutate if I hardcode the variable like this, but of course, I can't do it this way

const SET_ADDRESS_LASTUSED = gql`
  mutation {
    updateAddress(input: {
      where: {
        phone: "+12345678910"
      },
      data: {
        name: "ICanChangeMyName!"
      }
    }) {
      address {
        name
        phone
      }
    }
  }
`;

Please help. I've been debugging pointlessly for hours... I can always pass a variable to query using a similar way :(

Btw, I am using Strapi Server

Thanks in advance!

Reference: https://www.apollographql.com/docs/react/api/react/hooks/ https://strapi.io/documentation/developer-docs/latest/plugins/graphql.html#graphql