byte array must be in range 0 < M <= 32

bytes32_common_issues.md

byte array must be in range 0 < M <= 32

You can simply convert a string to a bytes32 format in kotlin or solidity

Solidity:

    function stringToBytes32(string memory source) private pure returns (bytes32 result) {
        bytes memory tempEmptyStringTest = bytes(source);
        if (tempEmptyStringTest.length == 0) {
            return 0x0;
        }
        assembly {
        result := mload(add(source, 32))
        }
    }

Kotlin:

    fun stringToBytes32(string: String): Bytes32 {
        val byteValue = string.toByteArray()
        val byteValueLen32 = ByteArray(32)
        System.arraycopy(byteValue, 0, byteValueLen32, 0, byteValue.size)
        return Bytes32(byteValueLen32)
    }

classes where error is thrown in web3j

package org.web3j.abi.datatypes;

/**
 * Statically allocated sequence of bytes.
 */
public class Bytes extends BytesType {

    public static final String TYPE_NAME = "bytes";

    protected Bytes(int byteSize, byte[] value) {
        super(value, TYPE_NAME + value.length);
        if (!isValid(byteSize, value)) {
            throw new UnsupportedOperationException(
                    "Input byte array must be in range 0 < M <= 32 and length must match type");
        }
    }

    private boolean isValid(int byteSize, byte[] value) {
        int length = value.length;
        return length > 0 && length <= 32 && length == byteSize;
    }
}

package org.web3j.abi.datatypes.generated;

import org.web3j.abi.datatypes.Bytes;

/**
 * Auto generated code.
 * <p><strong>Do not modifiy!</strong>
 * <p>Please use org.web3j.codegen.AbiTypesGenerator in the 
 * <a href="https://github.com/web3j/web3j/tree/master/codegen">codegen module</a> to update.
 */
public class Bytes32 extends Bytes {
    public static final Bytes32 DEFAULT = new Bytes32(new byte[32]);

    public Bytes32(byte[] value) {
        super(32, value);
    }
}

Another solution is to debug through these 2 specific classes and see the size of the byte[] that's being passed. After finding the descrepency you can alter the datasize enough to avoid the exception that's passed when trying to use these web3js libraries.

For creating a simple 32x hash to convert your string -> ByteArray you can use http://www.md5hasher.net/. This can be used as a final layer of encryption to your message before sending it to the contract.