session_start() error after activation

I’m receiving the following error after plugin activation:

Warning: session_start(): user session functions not defined in /srv/bindings/6a0d0cbd1d784cb087fa89bae4eb52ce/code/wp-content/plugins/give/includes/class-give-session.php on line 367 Fatal error: session_start(): Failed to initialize storage module: user (path: ) in /srv/bindings/6a0d0cbd1d784cb087fa89bae4eb52ce/code/wp-content/plugins/give/includes/class-give-session.php on line 367

Here’s my system report:

### WordPress Environment ###

Home URL: http://dev-matt-dean-2.pantheonsite.io
Site URL: http://dev-matt-dean-2.pantheonsite.io
WP Version: 4.7.4
WP Multisite: –
WP Memory Limit: 256 MB
WP Debug Mode: –
WP Cron: ✔
Language: en_US
Permalink Structure: /%postname%/
Show on Front: page
Page on Front: Home (#7)
Page for Posts: Travel Blog (#16)
Table Prefix Length: 3
Table Prefix Status: Acceptable
Admin AJAX: Accessible
Registered Post Stati: publish, future, draft, pending, private, trash, auto-draft, inherit, refunded, failed, revoked, cancelled, abandoned

### Server Environment ###

Hosting Provider: DBH: 10.223.192.204:16827, SRV: endpointd52659fb.chios.panth.io
Server Info: nginx/1.8.1
PHP Version: ❌ 5.5.24 – We recommend a minimum PHP version of 5.6. See: PHP Requirements in Give
PHP Post Max Size: 100 MB
PHP Time Limit: 120
PHP Max Input Vars: 10000
PHP Max Upload Size: 100 MB
cURL Version: 7.40.0, NSS/3.21 Basic ECC
SUHOSIN Installed: –
Default Timezone is UTC: ✔
fsockopen/cURL: ✔
SoapClient: ✔
DOMDocument: ✔
gzip: ✔
GD Graphics Library: ✔
Multibyte String: ✔
Remote Post: ✔
Remote Get: ✔

### Give Configuration ###

Give Version: 1.8.6
Upgraded From: 1.8.6
Test Mode: Enabled
Currency Code: USD
Currency Position: Before
Decimal Separator: .
Thousands Separator: ,
Success Page: http://dev-matt-dean-2.pantheonsite.io/donation-confirmation/
Failure Page: http://dev-matt-dean-2.pantheonsite.io/donation-failed/
Give Forms Slug: /donations/
Enabled Payment Gateways: Test Donation, Offline Donation
Default Payment Gateway: Test Donation
Admin Email Notifications: Enabled
Donor Email Access: Disabled

### Session Configuration ###

Give Use Sessions: Enabled
Session: Disabled

### Active Give Add-ons ###

### Other Active Plugins ###

Contact Form 7: by Takayuki Miyoshi – 4.7
Contact Form 7 Skins: by Neil Murray – 1.2
Fusion Builder: by ThemeFusion – 1.0.6
Fusion Core: by ThemeFusion – 3.0.6
Icegram – Popups, Optins, CTAs & lot more…: by icegram – 1.10.3
LayerSlider WP: by Kreatura Media – 6.3.0
Newsletter: by Stefano Lissa & The Newsletter Team – 4.8.9
Ninja Forms: by The WP Ninjas – 3.0.34.1
Rainmaker – The Best Readymade WP Forms Plugin: by icegram – 0.19
Slider Revolution: by ThemePunch – 5.4.2

### Inactive Plugins ###

Akismet: by Automattic – 3.1.5
bbPress: by The bbPress Community – 2.5.12
Email Subscribers & Newsletters: by Icegram – 3.2.9
Give – Form Field Manager: by WordImpress – 1.1.3
Hello Dolly: by Matt Mullenweg – 1.6
Ninja Forms – Layout & Styles: by The WP Ninjas – 3.0.18
The Events Calendar: by Modern Tribe, Inc. – 4.4.5
WooCommerce: by Automattic – 3.0.4
WP Reset: by WP Dev – 1.0.1

### Active MU Plugins ###

Pantheon: by Pantheon – 0.1

### Theme ###

Name: Avada
Version: 5.0.6
Author URL: http://themeforest.net/user/ThemeFusion
Child Theme: No – If you’re modifying Give on a parent theme you didn’t build personally, then we recommend using a child theme. See: How to Create a Child Theme