I'm attempting to migrate my v2 Lambdas to v3, and I'm having some trouble incrementing a value. Here's my v2 method:

  const params = {
    TableName: process.env.USER_TABLE_NAME!,
    Key: { UID },
    UpdateExpression: 'SET #numRatings = #numRatings + :increment',
    ExpressionAttributeNames: {
      '#numRatings': 'numRatings'
    },
    ExpressionAttributeValues: {
      ':increment': 1
    },
    ReturnValues: 'ALL_NEW'
  };

  return await DB.update(params).promise();

v3 method:

  const params = {
    TableName: process.env.USER_TABLE_NAME!,
    Key: {
      UID
    },
    UpdateExpression: 'set numRatings = numRatings + :increment',
    ExpressionAttributeValues: {
      ':increment': 1
    },
    ReturnValues: 'ALL_NEW'
  } as unknown as UpdateItemCommandInput;

  try {
    const response = await dbClient.send(new UpdateItemCommand(params));
    console.log('response', response);
  } catch (error) {
    console.error('error', error);
  }

I'm using TypeScript and VS Code gives this error:

Types of property 'Key' are incompatible.
    Type '{ UID: string; }' is not comparable to type '{ [key: string]: AttributeValue; }'.
      Property 'UID' is incompatible with index signature.
        Type 'string' is not comparable to type 'AttributeValue'

CloudWatch gives this unhelpful error:

Cannot read property '0' of undefined

I'm really confused as, as far as I can tell I have followed the documentation properly, their equivalent of "params" is defined as so:

export const params = {
  TableName: "TABLE_NAME",
  Key: {
    primaryKey: "VALUE_1", // For example, 'Season': 2.
    sortKey: "VALUE_2", // For example,  'Episode': 1; (only required if table has sort key).
  },
  // Define expressions for the new or updated attributes
  UpdateExpression: "set ATTRIBUTE_NAME_1 = :t, ATTRIBUTE_NAME_2 = :s", // For example, "'set Title = :t, Subtitle = :s'"
  ExpressionAttributeValues: {
    ":t": "NEW_ATTRIBUTE_VALUE_1", // For example ':t' : 'NEW_TITLE'
    ":s": "NEW_ATTRIBUTE_VALUE_2", // For example ':s' : 'NEW_SUBTITLE'
  },
  ReturnValues: "ALL_NEW"
};

My apologies if that's too many code examples but I wanted to be thorough. UID is a string. Thank you in advance for any help