How to fix "Your requirements could not be resolved to an installable set of packages" for installing Avalara?

I am trying to install Avalara for Magento 2 by following these documents- https://github.com/avadev/Avalara-AvaTax-for-Magento2/blob/master/docs/getting-started.md

Following what they have step by step for the composer install I end up with these errors-

Your requirements could not be resolved to an installable set of packages.

Problem 1
- The requested package avalara/avataxclient dev-integration/release-2.0.0 as 18.4.3.191 exists as avalara/avataxclient[17.12.0.147, 17.12.0.149, 17.5.0.67, 17.7.0.96, 17.8.1.120, 17.8.1.x-dev, 18.1.2.161, 18.1.2.x-dev, 18.1.x-dev, 18.10.5.260, 18.12.0, 18.2.0.167, 18.2.x-dev, 18.3.1.176, 18.4.3.191, 18.4.4.191, 18.5.1.208, 18.9.0.234, 19.1.1, 19.2.0, 19.3.0, 19.3.0.x-dev, 19.4.0, 19.4.0.x-dev, 2.17.1, 2.17.1.3, 2.17.2.43, 2.17.3.48, 2.17.4.58, dev-master, v19.1.1.x-dev, v19.2.0.x-dev] but these are rejected by your constraint.
Problem 2
- Installation request for classyllama/module-avatax 2.0.0-RC1 -> satisfiable by classyllama/module-avatax[2.0.0-RC1].
- classyllama/module-avatax 2.0.0-RC1 requires avalara/avataxclient ^18.4.3.191 -> satisfiable by avalara/avataxclient[18.10.5.260, 18.12.0, 18.4.3.191, 18.4.4.191, 18.5.1.208, 18.9.0.234] but these conflict with your requirements or minimum-stability.


Installation failed, reverting ./composer.json to its original content.

This is what my composer.json file looks like-

{
"name": "magento/project-enterprise-edition",
"description": "eCommerce Platform for Growth (Enterprise Edition)",
"type": "project",
"version": "2.3.1",
"license": [
    "proprietary"
],
"require": {
    "magento/product-enterprise-edition": "2.3.1",
    "composer/composer": "@alpha",
    "magento/extension-b2b": "^1.0",
    "boldcommerce/magento2-ordercomments": "~1.5.0",
    "amasty/orderattr": "^3.3",
    "ebizmarts/mailchimp-lib": "^3.0",
    "galacticlabs/customer-group-payment-filters": "^1.0",
    "amasty/module-elastic-search": "^1.3",
    "elasticsearch/elasticsearch": "~5.1",
     "msp/devtools": "^1.2",
     "zf1/zend-rest": "^1.12",
     "avalara/avataxclient": "dev-integration/release-2.0.0 as 18.4.3.191"
},
"require-dev": {
    "phpunit/phpunit": "~6.2.0",
    "squizlabs/php_codesniffer": "3.2.2",
    "phpmd/phpmd": "@stable",
    "pdepend/pdepend": "2.5.2",
    "friendsofphp/php-cs-fixer": "~2.10.1",
    "lusitanian/oauth": "~0.8.10",
    "sebastian/phpcpd": "~3.0.0"
},
"autoload": {
    "psr-4": {
        "Magento\\Framework\\": "lib/internal/Magento/Framework/",
        "Magento\\Setup\\": "setup/src/Magento/Setup/",
        "Magento\\": "app/code/Magento/",
        "Zend\\Mvc\\Controller\\": "setup/src/Zend/Mvc/Controller/"
    },
    "psr-0": {
        "": [
            "app/code/"
        ]
    },
    "files": [
        "app/etc/NonComposerComponentRegistration.php"
    ],
    "exclude-from-classmap": [
        "**/dev/**",
        "**/update/**",
        "**/Test/**"
    ]
},
"autoload-dev": {
    "psr-4": {
        "Magento\\Sniffs\\": "dev/tests/static/framework/Magento/Sniffs/",
        "Magento\\Tools\\": "dev/tools/Magento/Tools/",
        "Magento\\Tools\\Sanity\\": "dev/build/publication/sanity/Magento/Tools/Sanity/",
        "Magento\\TestFramework\\Inspection\\": "dev/tests/static/framework/Magento/TestFramework/Inspection/",
        "Magento\\TestFramework\\Utility\\": "dev/tests/static/framework/Magento/TestFramework/Utility/",
        "Magento\\ToolkitFramework\\": "dev/tools/performance-toolkit/framework/Magento/ToolkitFramework/"
    }
},
"minimum-stability": "stable",
 "repositories": {
    "0": {
        "type": "composer",
        "url": "https://repo.magento.com/"
    },
    "amasty": {
        "type": "composer",
        "url": "https://composer.amasty.com/enterprise/"
    },
    "xtento": {
        "type": "composer",
        "url": "https://repo.xtento.com"
    }

},
"extra": {
    "magento-force": "override"
},
"classyllama-avatax": {
    "type": "git",
    "url": "[email protected]:classyllama/AvaTax-REST-V2-PHP-SDK.git"
}
}

How can I get this to install properly?